OpenEVSE and wiring regs changes (722.531.2.101)

Does the OpenEVSE unit have any residual DC (fault) checks?
The latest regs 722.531.2.101 (Jan 2019) requires the use of either a Type B RCD (with built in dc capability/detection) or “RCD Type A and appropriate equipment that provides disconnection of the power supply in case of DC fault current above 6mA”.

I’d rather use type A RCDs as they are much cheaper than the rarer and more expensive type B RCDs

Type A RCDs will not trip with any levels of AC faults if they are saturated with even small levels of DC so it’s important to know…



I’ve read this document from pod point which is very enlightening.

I’ve also dug out my 18th Edition book and it says that either a Type-B RCD is used, or a Type-A RCD and another device used to disconnect if there is a >6mA DC fault current.

Looking at the install manual for the EmonEVSE, it says:

“The EmonEVSE contains an integral RCD which trips at 17mA AC and 15mA DC, this RCD will auto reset and will display status on the LCD.”

Also, there is no mention that the EmonEVSE integral RCD meets BS EN61008-1 / BS EN61009-1 BS EN60947-2 or BS EN62423 anywhere on the EmonEVSE documentation, So, unless anyone at OpenEVSE or OEM can say otherwise, I will have to presume a Type-B RCD is going to be needed to comply with regs.

Thanks for checking.
Even if the ac protection meets type A specs, the 15mA dc is too high.:frowning_face:
I’ll wait to see if there’s a definitive answer.
Interestingly Rolec also have a type A RCD (physical device not software) plus internal (software) 6mA DC detection.

Hi Guys,

The EmonEVSE and OpenEVSE contain an integrated software RCD / GFCI which trips at 17mA AC and 15mA DC in 25ms.

Currently, a Type B RCD is required to meet 6mA DC detection.

I will discuss with the OpenEVSE team if the DC trip level can be adjusted in software.

Update: A hardware modification would be required to change the trip point. The GFCI system was designed for AC detection.

From OpenEVSE: theory of operation OpenEVSE SAE J1772 Theory of Operation : Support

The current transformer coil detects any unbalanced current flowing through conductors passing through it. By passing both of the J1772 power cables through it, any current leaked to ground in the EV will result in a differential current within the CT. This will result in a voltage appearing at the input of the OP amp (diode D1 protects against excessive voltage in a run-away leakage event, such as a conductor short to ground). The second OP amp acts as a comparator and will “switch” from a low output to a high output when a threshold is exceeded. This output is fed as a fault indication into the CPU, which will register a ground fault and open the relay.

Just found this on the OpenEVSE site:

Looks like the mA trigger point is set in hardware…

You beat me to it! I was just updating my post to include this. You are correct the trip point is set in hardware but the processing of the trip is actuated in software.

I’m eyeing up the OpenEVSE for the day when I switch to an EV. I hope by the time I come to buy one, the OpenEVSE team can produce a modified version of the inbuilt RCD to trip at >6mA DC.
If the existing hardware cannot be modified suitably, then this device might be the answer:

If not, its either a Type-B RCD or the other device I have seen on the market is from Doepke: RCCBs Type A EV - Doepke UK Ltd and the item DFS4 040-2/0.03-A EV is being sold for £305 + VAT on Rapid Electronics website. That would also need a metal RCD enclosure housing and according to their info, a Type-A RCBO would still be needed upstream back at the consumer unit! Absolutely barmy :frowning_face:

I feel it is also worth updating the help guide online OpenEVSE Kit Build Guide - Guide | OpenEnergyMonitor and the install PDF once we know where we are regarding RCD requirements. It wouldn’t hurt to remind electricians about the changes in the 18th Edition in the online guides. It is likely that customers will buy an OpenEVSE and either DIY fit or get their local sparkie to fit it who does not install many EVSE installs and might not be fully aware of the requirements.

Points such as the RCD requirements, the need for an earth rod for a PME / TN-C-S install (making the install a “TT-island”) and also the Earth fault loop impedance Zs. Everything I have seen so far recommends it be under 200 ohms. However, I’ve also read that to prevent fussy cars like the Renault Zoe from refusing to charge, it should be under 150 ohms!

One last point for the curious, or those struggling to get some sleep. An excellent YouTuber, John Ward has produced a video explaining some of the 18th Edition specific changes for EVSE installations: BS7671 Section 722 Electric Vehicle Charging Earthing Arrangements - YouTube which is well worth watching if you’re in this game and need a reminder of Section 722 of the regs book!

Hi All
I think we’re missing something here.
I’m talking about DC faults.
The CR8420 is just a ferromagnetic core and won’t detect DC without checking for core saturation (usually done by modulating with a high frequency signal).

CR Magnetics CR8400 Series of Wire Lead Current Transformers are available in a wide range of sizes and materials to meet any AC current sensing needs.

Are we sure there’s any dc checking?

I’d also like to raise the issue of loss of earth detection in the regs (TT island or <70V checks) should I raise a new thread?

Thanks for putting us onto this. We are looking at options to integrate compliant DC leakage detection. The bender unit looks very interesting. Another options is Type A Residual Current Devices | Emobility

Type-B RCD’s with 6mA DC detection are expensive. I am able to obtain Chint NL210 RCD unit with 6mA DC detection for approx £130.

Good idea, I will put together a guide.

Indeed, your right about the Renault Zoe having a tighter requirement for earthing. I’ve also heard the 150 ohm figure being mentioned although I’ve struggled to find an official figure from Renault. Apparently using CanZE Android app + ODB2 Bluetooth dongle it’s possible to obtain lots more data from the Zoe, apparently the Zs reading is displayed on can bus when starting a charge and can be viewed using CanZE. I’m afraid I don’t have access to a Zoe to test this. I am however aware that I’ve never had trouble starting a charge from older public charge points in my LEAF, while PlugShare / ZapMap is full of comments from Renault owners unable to charge.

Ah yes, I’ve watched that. John is a legend!

You’re totally right, the current system was designed for residual AC monitoring. Sorry for the confusion. We recently had the unit tested using an RCD tester and the unit tripped at 15mA DC leakage. This reading is irrelevant since is nowhere close to the required 6mA.

I’m happy for this to be discussed on this thread since it’s applicable to 17th edition wiring. Are you referring to PEN fault detection? The EmonEVSE currently has got loss of earth detection but not PEN fault (protective earth and neutral) detection. Therefore, an earth-rod is currently required for outdoor installations, or where the EV under charge is located outdoors.

To comply with PEN fault detection if the voltage between the protective conductor and earth electrode is 70V rms we would need to disconnect the protective conductor from the EV within 5s. This would require an extra contactor to disconnect the protective conductor. This is something we’re considering integrating in future revisions. Currently, the recommended way round this is to install an earth rod (TT Island) on PME earthing setups and don’t use the PME earth.

Excellent to hear the RCD / 18th Edition issues are being looked into :smile:

I have to say I think 722.531.2.101 is not well thought out.
Why is it only EV chargers with the 6ma DC restriction. What about anything with possible DC faults (PV or even DC power supplies). They only need a few mA DC leakage to make RCDs/RCBOs inoperable.
Solving the very low probability of the failure of the PME system with a TT island is also a bit bonkers. I remember last century when we switched from TT to PME because house earth rods were susceptible to corrosion/lack of maintenance/damage etc.
Voltage operated protection was commonplace but considered inferior to RCDs when they came in.
Anyway, a bit off topic.

Maybe not
See Pod Point’s installation guide at

The new Pod Point Solo features an on-board safety
monitoring system to detect low voltage supplies and
potential earth-neutral faults, If such a condition is
encountered the charge cycle is ended or prevented and
the Pod-Point effectively becomes a double insulated
(class II) device. The vehicle becomes isolated from the
incoming supply and poses no risk to touch.This feature
removes the requirement for an earth electrode where
it may be ineffective or introduce further risk. The Pod
Point Solo unit (tethered or socketed) may be connected
directly to a TN-C-S (PME) earthing system without any
special arrangements, the new Pod Point solo complies
with regulation 722.411.1 (iii) of BS7671: 2018.

Also, if you talk to MyEnergi about the (long long overdue) Zappi 2 they also say they need no earth rod.

I for one would consider the risk of PME failure much lower than a domestic TT island’s earth rod failing so the Pod Point/Zappi solutions would be preferable.


I just want to charge my Leaf with my PV without mucking about with an expensive type B RCD and a TT earth rod…
I’d love an OpenEVSE sytem 'cos I love to support community activity
Whitby Esk Energy Community Hydro

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Hi Glyn

I’ve just had a thought about that.
I can’t see anything in the circuitry that checks DC so why do we think the unit tripped at all?
AFAICS the only residual current sensor is the CT and that would saturate and provide no voltage to the GFCI circuit.
Was the test pure DC or half wave AC?

Without knowing the technical details of these units, my guess is they have integrated GND disconnect contactor to isolate the EV if a PME fault occurs. I agree this protection mechanism is superior to a TT island but obviously requires hardware changes. It’s something we’re looking into for future hardware revisions.

I would also like to learn more about this. I will obtain more info and get back to you.

Forgive me for jumping in on the end of an interesting discussion (and for being a bit of a beginner)

I was planning to install a Zappi-2 (when/if it becomes available) but after many promises of an end user API over the last year my hopes were finally dashed with an email from one of their directors confirming they will not be developing one so I have cancelled my deposit.
Looking for alternatives I came across your EVSE which ticks all boxes but this thread concerns me.
I have a TN-CS site. While £550 is a saving over the Zappi, adding a £300 type B RCD is a bit of a sting in the tail. Is this just something I have to accept or is there any other option?
Apart from the RCD issue, is there a reason why your EVSE steps up and down in 1A steps? The Zappi seems to follow the export CT to within about 50W. Here I am going to expose my ignorance about the PWM signalling but is this something that can be improved in future?

Hi Steve,

I’ve just been in communication with our OLEV installer and their electrical supplier. They use a Chint NL210 Type-B RCD which meets the requirement not to be blinded by 6mA of DC leakage. This RCD costs less than £120. We will be getting stock of these RCD’s to sell with our units in the next week or so.

If you are interested in getting an EmonEVSE unit installed under OLEV I would recommend contacting EcoPlugg for a quote.

We are working on integrating DC leakage detection into our unit, but this is probably about 6-12 months away and will probably add about £100 at leat to the cost of the unit.

1A control resolution is the J1772 protocol supported by all EV’s. Zappie or any other EVSE won’t be able to control the charge rate at any higher resolution since this is a hard limitation of all EV’s. Also the minimum charging current of J1772 is 6A approx 1.4kW.

For more info on J1772 see: OpenEVSE SAE J1772 Theory of Operation : Support

Thank you for the fast response Glyn. I certainly will look out for your affordable type-B RCDs. Will they appear on the shop as optional accessories? Sadly I cannot take advantage of the OLEV grant as I have used my allocation, first with a PodPoint five years ago and the second time with a Zappi about two years ago.
The Zappi really does manage higher resolution changes, certainly with the Golf and the Kona we run here but it isn’t a huge issue as we now have a couple of Powerwall IIs which can absorb/support the gaps. It may be that some cars go beyond the J1772 PWM standard although I concur with the 6A lower limit. That is where the Zappi cheats a bit, allowing you to set a %age of “greenness” permitting EVSE startup when PV is <6A.
I’ll temporarily disable the batteries the next time we get a sunny day and plot the PV against the export and post it here.
I have never tried playing with MQTT so am looking forward to control the EVSE max rate based on the PWs SoC and the Octopus HH tariff.

Yes, hopefully in the next week. I’m just waiting on supplier to finalise pricing.

Actually, I think you could be right. The PWM could be controller to a higher resolution. The limiting factor would be the onboard charger. I will do some testing and investigate if the openevse controller could in the future be firmware upgraded to support higher resolution.

Yes, there are lots of possibilities for automation and integration. Using NodeRED is a popular option.

Hi all
Came across this link
Voltimum news
Which states

From January 2018, IC-CPDs manufactured to IEC 62752:2016 used in Mode 2 charging cables , had to include the facility to detect DC residual currents and disconnect if > 6mA DC

This would make it difficult to sell plug-in versions of OpenEVSE without the type B rcd.

Look forward to £120 rcds as I can only see them over £200 :grinning:

Interesting, thanks for the link. The OpenEVSE is not sold as a mode 2 unit. We are working on integrating DC current leakage detection. In the meantime we have sourced some reasonably priced type-B RCDs:

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Apologies in advance, if my post doesn’t make any sense.
Like many others I have been looking at openEVSE as an option, but worry about the need for TT island’s earth rod.

I noticed this article about amendments to the 18th edition, which I am sure you are very well aware:

Is this something the OmonEVSE unit is likely to support?